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"This statement was nothing more than a press communique," the parliament lawyer told MEPs in the civil liberties committee.

"This statement is not a binding agreement."

He noted the statement came without any signatures and was not published in the Official Journal of the European Union.

"It is very difficult to conclude that both the European Union and Turkey wanted to be legally bound under international law by this declaration," he said.

The distinction is important because the European Parliament is obliged to sign off on international agreements.

He said the language used in the statement suggests the two sides did not want an international accord.

"It is really a long way from the drafting standards of any international agreement," he said.

Despite the lack of clarity behind the statement, it still conforms to EU law, he noted.

Parliament will still have to sign off on visa-waiver plans and other issues like the budget and the resettlement of people on the one-to-one migrant swap deal.

The statement was hatched by EU heads of state and Turkey's former prime minister Ahmet Davutoglu in a wider effort to stem the flow of migrants to Greece.

Davutoglu had rewritten a draft version en route from Turkey to Brussels, which he then presented to stunned EU leaders in early March.

Agreement, statement, what is it?

MEPs at the committee appeared increasingly agitated by the whole plan, with Swedish liberal Cecilia Wikstroem describing it is as a farce.

She accused the EU commission and the Council, representing member states, of switching tactics.

Before they called it an "agreement" but now they call it a "statement", she said.

"They now realise that if this was an indeed a binding agreement between EU and Turkey, in an area where this parliament has co-decision, namely migration and budget, then the parliament also a constitutional obligation to either accept or reject this agreement," she told MEPs.

Dutch liberal Sophie In't Veld drew a similar conclusion.

She said the EU commission had until the 19 April used the term "agreement" and then switched it with "statement".

"I think the commission realised very well the legal implications of that term," she said.